This invention relates generally to systems for digital information processing, and, more particularly, relates to apparatus and methods for providing real-time monitoring, control, and simulation of industrial processes.
Modern industrial plants, including nuclear and fossil-fuel power plants, refineries, and chemical plants, typically utilize distributed monitoring and control systems which generate significant numbers of plant process measurement values and alarm status signals. Experience has demonstrated that human operators are unable to continuously monitor and interpret large volumes of data, especially during process upset conditions. The results of such operator overload range from non-optimal plant operation to disastrous process upset, with concomitant economic loss.
A number of computer-based systems have been proposed or developed to address this problem, and to provide monitoring and control of industrial processes. Certain such systems utilize expert systems for evaluating process parameters in accordance with knowledge expressed in the form of rules. These systems have been applied to interpretation of sensor data, operational fault diagnosis, process disturbance handling, prediction of consequences of changes, and process optimization during plant operation, start-up, and shutdown. The following U.S. and foreign patents provide examples of such systems.
______________________________________ Kemper et al. U.S. Pat. No. 4,644,479 Hardy et al. U.S. Pat. No. 4,648,044 Thompson et al. U.S. Pat. No. 4,649,515 Clemenson U.S. Pat. No. 4,675,829 Gallant U.S. Pat. No. 4,730,259 Natarajan et al. U.S. Pat. No. 4,752,890 Ashford et al. U.S. Pat. No. 4,754,409 Heichler U.S. Pat. No. 4,757,506 Ashford et al. U.S. Pat. No. 4,763,277 EPO 184,087 EPO 184,088 EPO 205,873 PCT/WO87 6,371 DE 3,621,859 JP 63 209,917 ______________________________________
The Kemper patent discloses apparatus including a set of sensors, which can be distributed about an industrial plant, for providing data to a computer. The computer utilizes an expert system which reads and processes the output of the sensors to obtain indications of sensor output change, confirmation of sensor readings, and malfunction indications based on sensor readings.
The Hardy et al. patent discloses an expert system for constructing a knowledge base utilizing facts, rules, and meta-facts which control the application of rules to solve specific problems.
Thompson et al. discloses apparatus for fault diagnosis and control, including elements for generating a knowledge base for the controlled process and storing the knowledge base in memory as a list including domain specific rules in evidence-hypothesis form.
Ashford et al. '409 discloses a method for collecting data from external processes and applying the data for use in an expert system. The expert system rulebase includes specific definitions of processes which are available to the expert system. The method permits data to be collected in response to location, time, and other attribute parameters supplied by the expert system.
Ashford et al. discloses an expert system which generates answers to system-generated inquiries based on related information previously obtained or generated by the system. The system utilizes action attributes that can be attached to rule tree nodes which provide an answer to a class inquiry, based on processing selected dependent nodes.
Natarajan et al. discloses an expert system including a sub-system for optimizing the scanning of rule lists in programs containing a sequential decision chain with independent or mutually exclusive outcomes. The sub-system executes iterative observations of the execution of the decision chain to optimize the ordering of rule application.
The PCT/WO87/06371 publication discloses an expert system for processing data to produce signals indicative of the condition of a monitored process. The expert system provides an adaptive pattern recognition utility which can be trained to recognize combinations of input data representative of particular fault conditions.
The JP 209917 publication discloses an expert system for controlling industrial processes. The system includes input means for reading fault data, a knowledge base for storing fault data and causation data for selected sub-processes, a set of diagnosticrule data representative of confidence levels for diagnostic results obtained by applying the diagnostic rule data, and a rule driven engine for calculating the effects of decisions rendered for selected fault events, based on the knowledge base.
The DE 3,621,859 publication discloses an expert system in which each problem solution is stored as a value representative of the sum of problem oriented criteria, under the control of a value code.
Clemenson, Gallant, Heichler, EPO 184,087, EPO 184,088, and EPO 205,873 also disclose rule-based decision systems.
Another process control system is disclosed in Moore, "Expert Systems in Process Control", TAPPI Proceedings, 1986. The Moore publication discusses time stamping of measured or inferred values, and assignment of currency intervals to variables.
Certain conventional process control systems, however, are unable to provide real-time processing of the large numbers of measurements generated by distributed control systems. These systems thus can not provide advisory information to an operator in real-time. Some prior art control systems are limited by conventional expert system configurations, which exhaustively search rule bases and fire all rules, thereby expending significant processing time. This problem is especially apparent in applications requiring large knowledge bases for accurate implementation.
It is accordingly an object of the invention to provide methods and apparatus for real-time monitoring, information, advice, control and optimization of plant processes, utilizing streamlinedrule processing.
Existing distributed sensor systems provide only a limited bandwidth channel between the distributed sensors and the processor. It is therefore undesirable to have unnecessary data transmitted into the system. Notwithstanding this limitation, however, conventional control systems, typically sample all distributed process sensors on a regular basis. This scanning leads to saturation of the available communications bandwidth with measurement values and alarms, and causes overloading of the distributed process sensor system with requests for information. Communications channel overload is especially troublesome because data quickly becomes invalid under overload conditions. While it is desirable to have data available and current when a given rule requiring the data needs to be evaluated--rather than to request data on a piecemeal basis as required by a given rule--many conventional control systems do not optimize data requests in this manner.
It is therefore another object of the invention to provide real-time methods and apparatus which optimize data requests and utilization of communications channel bandwidth.
A further object of the invention is to provide real-time control methods and apparatus which can integrate into existing plant control systems. Information from databases, MIS systems, supervisory systems and simulators may be required for analysis, in addition to data and alarm information from existing plant control systems.
Still another object of the invention is to provide real-time control methods and apparatus which can be event driven--i.e., in addition to requesting data, the system responds to interrupts by alarms and process events. A further object is to provide methods and apparatus in which the control process is not interrupted by secondary processes such as data plotting or system maintenance.
An optimal real-time process control system should provide flexibility in data and message presentation, so that users can configure operator interfaces for message and data presentation in accordance with their current control strategy and operator expertise. The control system should be capable of transmitting advisories back to the existing local control system for use in an operator's message page or application window.
Additionally, the control system should operate on an industry accepted, commonly available, general purpose computer system, should utilize software coded in an industry accepted language, but should not require programmers for operation or specification, or knowledge engineers for development. Certain process control expert systems fail to provide a user/knowledge base interface which facilitates programming and knowledge base restructuring by on-site personnel. It is thus another object to provide real-time methods and apparatus with enhanced user- and external-interface capabilities and characteristics.
Further objects of the invention are to provide real-time control methods and apparatus which can operate during all states of a process from start-up to shut-down; recognize and appropriately process data of uncertain, missing or diminished validity; self-recover after a power interruption without data loss and maintain continuous operation even when a fault occurs; compare a process with a simulator model of the process while on-line; and permit the imposition of access security restrictions.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.